The present invention relates to a thermally fused integral ferrule and its manufacturing method, and a fiber array manufacturing method using the thermally fused integral ferrule.
Fiber alignment parts include fiber arrays that connect optical parts such as quartz waveguides to fibers; and MT connectors that connects fibers together.
The material of the fiber array is generally glass or silicon due to the low thermal expansion coefficient of the connected optical part, for example, a waveguide. Inexpensive quality glass materials have recently been developed, so glass is now the main material of the fiber array.
In a conventional resin assembled fiber array using V-shaped grooves, fibers are mounted on V-shaped grooves in a V-shaped groove substrate, pressed against the grooves by a fiber presser substrate, and stuck and fixed thereto with resin. By setting the depth of the V-shaped grooves so that the heads of the fibers protrude from the top of the V-shaped grooves and pressing the heads using the fiber presser substrate, the fibers can each be contacted accurately with the respective V-shaped groove at two points and can thus be arranged accurately.
Since the fibers, V-shaped groove substrate, and fiber presser substrate are simultaneously stuck and fixed together, these components are generally assembled using a resin adhesive that provides an excellent operability.
In the long run, however, the use of the adhesive may cause the stuck portion between the V-shaped groove and fiber presser substrates to be degraded when an environmental condition such as humidity or heat changes.
In addition, since the fiber presser substrate is mounted on the V-shaped grooves, the substrates must be aligned, but this operation is complicated and requires high costs.
Furthermore, since the fiber contacts each V-shaped groove at two points, the accuracy of the arrangement of the fibers after assembly depends on the accuracy of the V-shaped grooves. This accuracy, however is also affected by a difference in fiber diameter (for example, in a 16-fiber array, the difference in diameter among all the 16 fibers).
In view of this point, to maintain long-term reliability, attempts have been made to metallize the substrates so as to use solder for adhesion. In this case, however, the high operating temperature and fluidity of solder makes assembly very difficult, stress may be caused by a difference in thermal expansion between the metallized substrates and glass, and the cost of the solder is high.
Furthermore, a technique for solving the problem associated with the alignment between the V-shaped groove substrate and the fiber presser substrate is known wherein the V-shaped grooves are sized to allow each fiber to sit within the respective groove instead of contacting each groove at two points, wherein the V-shaped groove and fiber presser substrates are stuck together with resin prior to the insertion of the fibers so that the fibers can be later inserted between them. If an adhesive or solder is used to stick the substrates together, a problem similar to that described above may occur.
As shown in FIG. 7, a connector 30 in which normal 125-xcexcm fibers are arranged at a 250-xcexcm pitch is generally used as an MT connector, wherein optical fiber insertion holes 36 are formed at a 250-xcexcm pitch. Optical fibers are inserted into the optical fiber insertion holes 36, and the holes are formed with a very strict clearance in order to arrange the fibers accurately. The holes are about 127 xcexcm for the normal 125-xcexcm optical fibers. It is very difficult to insert optical fibers into these holes, so 250-xcexcm pitch semicircular guide grooves 32 are provided to allow optical fibers to be inserted efficiently. The guide grooves 32 are continuously joined with the optical fiber insertion holes 36 via conical tapers 34 to allow optical fibers to be inserted easily.
Thus, resin injection-molded connectors that are normally inexpensive and provide a high dimensional accuracy have generally been used as MT connectors. Since, however, such a connector is composed of resin, it is not optimal for connection with, for example, a quartz waveguide due to its high thermal expansion.
Consequently, the MT connector is desirably formed of glass, but it is conventionally difficult to form a plurality of circular holes in glass using the arrangement accuracy of the MT connector. As a result, this technique has not been industrially realized.
The present invention is provided in view of this conventional problem, and its object is to provide an inexpensive ferrule that has high junction strength, watertightness, and productivity, and its manufacturing method, as well as a fiber array manufacturing method.
This invention provides a thermally fused integral ferrule in which a first glass substrate is at least partly combined with a second glass substrate unitarily by means of thermal fusion, wherein the first glass substrate includes optical-fiber fixing V-shaped grooves on its side opposed to the second glass substrate and also includes on the optical-fiber fixing V-shaped groove in the first glass substrate, a guide section having a predetermined void between the first and second glass substrates.
According to this invention, the maximum surface roughness (Rmax) of the internal surfaces of the first and second glass substrates is preferably between 0.2 and 2.0 xcexcm, and the area of the surface to be thermally fused of each of the first and second glass substrates is preferably 0.01 mm2or more.
In addition, this invention provides a method for manufacturing a thermally fused integral ferrule comprising: contacting a surface to be thermally fused of a first glass substrate in which optical-fiber fixing V-shaped grooves are formed with a surface to be thermally fused of a second glass substrate, and thermally fusing said surfaces of the first and second glass substrates at a temperature of (Tg1xe2x88x92100) to (Tg2+150)xc2x0 C. (where Tg1 is the glass transition temperature of one of the first and second glass substrates that is higher than that of the other and Tg2 is the lower glass transition temperature).
Moreover, this invention provides a method for manufacturing a thermally fused integral ferrule, comprising forming a film of a glass frit on a surface to be thermally fused of a first glass substrate in which optical-fiber fixing V-shaped grooves are formed or on a surface to be thermally fused of a second glass substrate, contacting the surfaces of the glass substrates together, and thermally fusing the surfaces of said glass substrates at a temperature of (Tg3) to (Tg4+150)xc2x0 C. (where Tg3 is the glass transition temperature of the glass frit and Tg4 is the glass transition temperature of the first glass substrate).
According to this manufacturing method, the maximum surface roughness (Rmax) of the surface to be thermally fused of each of the first and second glass substrates is preferably 0.5 xcexcm or less.
Moreover, this invention provides a fiber array manufacturing method using the thermally fused integral ferrule, comprising following the steps (a)-(e):
(a) arranging the tips of optical fibers over the guide section on the optical-fiber fixing V-shaped grooves;
(b) lowering the tips of the optical fibers onto the optical-fiber fixing V-shaped grooves;
(c) inserting the optical fibers into the thermally fused integral ferrule while allowing the optical-fiber fixing V-shaped grooves to guide the tips of the fibers; and
(d) applying and filling a first liquid adhesive to and in the entire thermally fused integral ferrule;
(e) solidifying the first liquid adhesive.
If a thermally fused integral ferrule is used in which the second glass substrate is thermally fused in such a way that there is an open space over the guide section on the optical-fiber fixing V-shaped grooves in the first glass substrate while only the optical-fiber fixing V-shaped grooves are covered, the fiber array manufacturing method desirably comprises the following steps (f) and (g) subsequent to the step (e):
(f) covering a covered optical fiber with a second liquid adhesive; and
(g) solidifying the second liquid adhesive.
In addition, according to the fiber array manufacturing method, it can have prior to the step (a) the step of applying a liquid adhesive to the optical-fiber fixing V-shaped grooves in the first glass substrate or to the optical fibers.